Weight limit notice

The little notice in a lift or elevator that tells you the number of persons and the total weight allowed, before the lift is over-loaded. Something like "16 Persons or 1040 kg". I find myself averaging the the weight allowed, and wondering if we are all supposed to be 65 kg? Or estimating the weights of other passengers in the lift with me to work out how close we are to the limit, or if the little buzzer will go off before we have 16 people?